A magnetic sensor capable of detecting the change of the magnetic field is developed as a measuring device and used in various applications such as the galvanometer, the magnetic encoder and the like. One example of such a magnetic sensor is disclosed in the following Patent Document 1 in which a GMR element (Giant Magneto Resistive element) is used as the element for detecting the change of the magnetic field. The GMR element is a kind of element in which the output resistance value changes according to the input magnetic field, and the change of the magnetic field to be detected can be measured based on the output resistance value.
As one example showing the specific configuration of the magnetic sensor where the GMR element is used, as described in Patent Document 1, four GMR elements are provided in the substrate to form a bridge circuit. As such, the change of the resistance value in the GMR element is detected by detecting the differential voltage in the bridge circuit, wherein the change of the resistance value in the GMR element is with the change of the magnetic field which becomes a detection object. In this respect, a sensor that is highly sensitive to the change of magnetic field has been provided.
In particular, as an element to detect the change of magnetic field, a GMR chip (the chip for detecting magnetic field) is provided in the magnetic sensor as disclosed in Patent Document 1, wherein the GMR chip utilizes the spin valve typed GMR elements (Giant Magneto Resistive element) in which the output resistance value changes depending on the direction of the input magnetic field. As such, each GMR element is magnetized fixedly in a specific direction in one surface so as to detect the magnetic field in the specified direction. Here, in order to downsize the GMR chip and also to lower the deviation in each resistance value, four GMR elements which have already formed the bridge circuit are provided on one GMR chip. Thus, all four GMR elements are magnetized fixedly in the same direction.
FIG. 1 and FIG. 2 illustrate the characteristic of the GMR element. First of all, the characteristic of the GMR element used in the present invention will be described with reference to FIG. 1 and FIG. 2. The GMR element is the GMR element (Giant Magneto Resistive element) made in the spin valve type in which output resistance value changes depending on the direction of the input magnetic field. As such, in FIG. 1 and FIG. 2, the relationship between the approach angle and the resistance value is shown, wherein the approach angle refers to the angle of magnetic field H relative to the GMR element.
In the example as shown in FIG. 1, GMR elements are formed on the upper surface of GMR chip 1. The GMR elements are arranged in such a manner that they are magnetized fixedly in the direction indicated by arrow A. Thus, the magnetic field in the direction as indicated by arrow A can be detected.
In FIG. 1, the GMR elements are arranged in magnetic field H that enters in the direction perpendicular to the form surface of the GMR elements. In this respect, the resistance value of the GMR element turns to “R0” as shown in FIG. 2. In contrast, if the direction of magnetic field inclines, the incidence angle of magnetic field H relative to the GMR element surface deviates from the perpendicular direction with an angle of i.e., −Δθ or +Δθ, as shown in FIG. 1 with dotted lines, wherein Δ(Delta) refers to the variation. In this way, the GMR element is magnetized fixedly in one direction and the resistance value of the GMR element changes when the direction of the magnetic field changes with respect to said direction, as shown in FIG. 2. As such, the GMR element has the following characteristic. If the resistance value is defined as R0 when the magnetic field enters in a perpendicular direction, the resistance value will have substantial change when the direction of the magnetic field H inclines with a tiny angle.
FIG. 3 and FIG. 4 show the configuration of the conventional magnetic sensor. When the magnetic field in one direction is detected by using a GMR chip where the bridge circuit as described above has been formed, magnetic body 21 which changes the direction of the magnetic field input to the GMR element is provided in the vicinity of the element forming part where the GMR elements in pair that are adjacent but not connected to each other in the bridge circuit are provided at almost symmetrical positions, as described in Patent Document 1.
Further, magnetic body 21 can change the external magnetic field in one direction into a different direction between the GMR elements. In this way, four GMR elements inside the bridge circuit are provided in such a manner that the magnetic field comes out in the direction in which the magnetization is fixed relative to one and comes out in the opposite direction relative to another one. As such, a high differential voltage is output from the bridge circuit, and the magnetic field in one direction can be detected in precision.
FIG. 5 is a schematic view showing the magnetic field H introduced to the GMR element parts 11 and 12 through magnetic body 21 as described in Patent Document 1. The magnetic field bends due to magnetic body 21, and the component of the magnetic field is generated in the GMR element parts 11 and 12 in the direction of the induced magnetic field (magnetic field component in the X-axis direction) and the resistance value of said GMR element changes. Thus, the sensor is provided which is highly sensitive to the change of the magnetic field. In addition, in the following description, the direction parallel to that where the GMR element is magnetized fixedly is defined as the X-axis direction, and the direction which is perpendicular to that where the GMR element is magnetized fixedly and also is located on the surface where the GMR elements are formed is defined as the Y-axis direction. Further, the direction perpendicular to the surface where the GMR elements are formed is defined as the Z-axis direction.
Patent Document 2 has disclosed a sensor in which several magnetic bodies are provided for the magnetoresistance effect element to convert the external magnetic field in the vertical direction into magnetic field component in the horizontal direction so that the component of the magnetic field entering in the vertical direction is detected.